The invention relates to parts coated with a protective coating, and to methods of fabricating such parts.
At present, within the hottest parts in turbine engines, only superalloys based on nickel are used on an industrial scale. Although such nickel-based superalloys are coated with a thermal barrier system, their utilization temperature may be limited to 1150° C. because of the proximity of their melting point.
Recent research work has focused on using new materials based on refractory metals capable of being used at temperatures higher than the utilization temperatures of nickel-based superalloys. These families of materials are commonly referred to as: refractory metal matrix composite materials.
Among the solutions that have been found, niobium-based alloys seem to be particularly promising for replacing or being used in addition to existing nickel-based superalloys. These various alloys have the advantage of presenting melting points that are higher than those of existing superalloys. Furthermore, niobium-based alloys can also advantageously present densities that are relatively low (6.5 grams per cubic centimeter (g/cm3) to 7 g/cm3, in comparison with 8 g/cm3 to 9 g/cm3 for nickel-based superalloys). Such alloys can thus advantageously serve to reduce significantly the weight of turbine engine parts, e.g. the high pressure turbine blade sets, because of their low density and because of their mechanical properties that are close to the mechanical properties of nickel-based superalloys at temperatures close to 1100° C.
Such niobium-based alloys may generally comprise numerous addition alloying elements such as silicon (Si), titanium (Ti), chromium (Cr), aluminum (Al), hafnium (Hf), molybdenum (Mo), or tin (Sn), for example. These alloys present a microstructure constituted by a niobium matrix (Nbss) reinforced by addition elements dissolved in solid solution. This phase provides the alloys with acceptable toughness at low temperature. The refractory matrix is associated with intermetallic precipitates, often refractory metal silicides of composition and structure that may vary depending on the addition elements (M3Si, M5Si3).
In spite of the large amounts of progress that have been made concerning the composition of alloys seeking to increase their ability to withstand oxidation at high temperature, this ability may not suffice for envisaging a direct industrial application.
There therefore exists a need to have novel materials presenting both good mechanical properties (concerning toughness when cold and creep at high temperature for moving parts) and also good resistance to corrosion and to oxidation at very high temperature.
There also exists a need to have novel methods enabling such materials to be obtained.